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Avoid unchecked list indexing in JSON encoder #9431

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Merged
youknowone merged 1 commit into from
Oct 28, 2026
Merged

Avoid unchecked list indexing in JSON encoder #9431

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19 changes: 14 additions & 5 deletions crates/stdlib/src/json.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -1102,7 +1102,7 @@ mod _json {
/// collection on every step (rather than working off a
/// pre-collected snapshot) so that a `default()`/nested-encoder
/// callback that shrinks the list mid-encode is observed the same
/// way CPython's `PySequence_Fast`-free direct indexing observes it
/// way CPython's live sequence iteration observes it
/// (see `test_encode_mutated`: deleting the last element on every
/// callback call causes encoding to stop early once the shrinking
/// list's length catches up with the read cursor).
Expand All @@ -1113,7 +1113,7 @@ mod _json {
out: &mut Wtf8Buf,
vm: &VirtualMachine,
len: impl Fn() -> usize,
get: impl Fn(usize) -> PyObjectRef,
get: impl Fn(usize) -> Option<PyObjectRef>,
) -> PyResult<()> {
if len() == 0 {
out.push_str("[]");
Expand All @@ -1128,7 +1128,9 @@ mod _json {
};
let mut i = 0;
while i < len() {
let value = get(i);
let Some(value) = get(i) else {
break;
};
if i == 0 {
self.push_newline_indent(out, new_level);
} else {
Expand Down Expand Up @@ -1311,11 +1313,18 @@ mod _json {
out,
vm,
|| list.borrow_vec().len(),
|i| list.borrow_vec()[i].clone(),
|i| list.borrow_vec().get(i).cloned(),
)
} else if let Some(tuple) = obj.downcast_ref::<PyTuple>() {
let slice = tuple.as_slice();
self.encode_list(obj, level, out, vm, || slice.len(), |i| slice[i].clone())
self.encode_list(
obj,
level,
out,
vm,
|| slice.len(),
|i| slice.get(i).cloned(),
)
} else if let Some(dict) = PyAnyDict::from_object(obj) {
self.encode_dict(obj, dict, level, out, vm)
} else {
Expand Down
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